How to set the focus to the text Box when the error throws

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C#

Hi,
I want to set a focus to the text box when the error throws. I am using calling this class from some other class.Here is the code

public string CustomerSubmission
    {
        get
        {
            return _customerSubmission;
        }
        set
        {
            try
            {
                DateTime CustomerSubmission = Convert.ToDateTime(UserUtil.ConvertDate(value.ToString().Trim()));
                if (value.ToString().Trim() == "")
                {
                    throw new Exception(Message.Blank("Customer Submission Date"));                    
                    
                }
                else if (!UserUtil.IsDateinDDMMYYYYFormat(value))
                {
                    throw new Exception(Message.InvalidDate("Customer SubmissionDate"));
                }
                else if (CustomerSubmission > DateTime.Now)
                {
                    throw new Exception(Message.DateShouldBeLessThan("Customer Submission Date"));
                }   
                _customerSubmission =  UserUtil.ConvertDate(value.ToString().Trim());
            }
            catch (Exception ex)
            {
                throw;
            }
        }
    }

Thanks in advance